1. Field of the Invention
The present invention relates to an inkjet ink composition, an ink set, and an image forming method.
2. Description of the Related Art
Aqueous paints and inks have increasingly been used in recent years due to increased needs for, for example, resource conservation, environment preservation, and enhanced operational stability. The properties that the aqueous paints and aqueous inks are required to possess include fluidity, storage stability, gloss of a film formed therefrom, clearness, and coloring power, similarly to the case of oil-based paints and oil-based inks. However, most pigments have remarkably inferior adaptability (e.g., pigment dispersibility) to aqueous vehicles, compared to adaptability thereof to oil-based vehicles. Therefore, satisfactory quality cannot be obtained using usual dispersion methods. Although use of various additives, such as aqueous pigment-dispersing resins for aqueous systems and surfactants, has so far been studied, aqueous paints or aqueous inks that possess all of the properties described above and that are comparable to existing oil-based paints or oil-based inks having high quality have not been obtained.
In order to solve the problems, Japanese Patent Application Laid-open (JP-A) No. 2001-329199 discloses an aqueous ink composition containing a coloring agent coated with a water-insoluble polymer as a colorant and polymer particles, for example. An inkjet ink in which the aqueous ink composition is used is described to have excellent water resistance, abrasion resistance, marker resistance, and printing properties.
JP-A No. 2006-273892 discloses an ink composition containing at least a coloring agent coated with a water-insoluble polymer as a colorant and a resin emulsion as an additive, the water-insoluble polymer having a weight average molecular weight of from 50,000 to 150,000, the resin emulsion containing at least a polymer of which constituent component has the same structure as that of the water-insoluble polymer and which has a weight average molecular weight that is from 1.5 times to 4 times greater than that of the water-insoluble polymer. The ink is described to have favorable glossiness and abrasion resistance.
JP-A No. 10-195352 discloses an inkjet ink composition containing an aqueous carrier medium, a colorant that is insoluble in the aqueous carrier medium, and a hydrosol polymer. The ink composition is described to have stability and low viscosity.